Louisiana State University LSU Digital Commons LSU Master's eses Graduate School 1-24-2018 Evaluation of Growth Characteristics, Yield, Marketability and Nitrate Levels of Leuce (Lactuca sativa L) Cultivars Produced in South Louisiana William D. Aſton Louisiana State University and Agricultural and Mechanical College, waſt[email protected]Follow this and additional works at: hps://digitalcommons.lsu.edu/gradschool_theses Part of the Agriculture Commons is esis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's eses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. Recommended Citation Aſton, William D., "Evaluation of Growth Characteristics, Yield, Marketability and Nitrate Levels of Leuce (Lactuca sativa L) Cultivars Produced in South Louisiana" (2018). LSU Master's eses. 4382. hps://digitalcommons.lsu.edu/gradschool_theses/4382
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Louisiana State UniversityLSU Digital Commons
LSU Master's Theses Graduate School
1-24-2018
Evaluation of Growth Characteristics, Yield,Marketability and Nitrate Levels of Lettuce(Lactuca sativa L) Cultivars Produced in SouthLouisianaWilliam D. AftonLouisiana State University and Agricultural and Mechanical College, [email protected]
Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses
Part of the Agriculture Commons
This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSUMaster's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected].
Recommended CitationAfton, William D., "Evaluation of Growth Characteristics, Yield, Marketability and Nitrate Levels of Lettuce (Lactuca sativa L)Cultivars Produced in South Louisiana" (2018). LSU Master's Theses. 4382.https://digitalcommons.lsu.edu/gradschool_theses/4382
EVALUATION OF GROWTH CHARACTERISTICS, YIELD, MARKETABILITY AND
NITRATE LEVELS OF
LETTUCE (LACTUCA SATIVA) CULTIVARS PRODUCED IN SOUTH LOUISIANA
A Thesis
Submitted to the Graduate Faculty of the
Louisiana State University and
Agricultural and Mechanical College
in partial fulfillment of the
requirements for the degree of
Master of Science
in
The School of Plant, Environmental and Soil Sciences
by
William Daynne Afton
B.S., Louisiana State University, 2011
May 2018
ii
ACKNOWLEDGMENTS
I would like to express my sincere appreciation for my major professor, Dr. Kathryn “Kiki”
Fontenot. I am forever indebted to her for providing me the opportunity to pursue a Master of Science
degree in Horticulture. It was through her friendship, guidance, and supervision that helped me to
realize my passion to inform everyday people about agriculture and the current industry. I would also
like to express my sincere appreciation for my remaining committee members, Dr. Jeff Kuehny and
Dr. Carl Motsenbocker. None of this would have been possible without their support and guidance.
In addition to my committee, I would also like to thank others whose help and guidance helped
throughout my coursework and research projects. First, I would like to thank my parents, Alan and
Marlene Afton for their words of encouragement throughout the graduate school process. I would like
to thank all the Burden staff, volunteers, graduate assistants and student workers who helped during the
lettuce harvest. I would like to especially thank Keith Lewis, Adley Peltier, Andrew Barker, Mike
Steele and Rick Hamilton, Carly Gillett, Reeve LeGendre, Mathew Indest, Mark Wilson, and Julie
Nieto. I would also like to thank all the professors and administrative personnel in the JC Miller Hall
including: Amy Blanchard, Dr. Charlie Johnson, Dr. Paul Wilson and Dr. Jimmy Boudreaux for all of
their advice and encouragement. Last but definitely not least, I would like to thank all of the producers
I have met and spoke with while working with Dr. Fontenot. It is for their advancement in which I
strive.
iii
TABLE OF CONTENTS
ACKNOWLEDGMENTS ........................................................................................................................ ii
LIST OF TABLES ................................................................................................................................... iv
ABSTRACT ............................................................................................................................................. v
CHAPTER 1: INTRODUCTION ............................................................................................................. 1 History of Lettuce ......................................................................................................................... 1
Classification ................................................................................................................................ 2 Nitrates .......................................................................................................................................... 2 Nitrate Accumulation .................................................................................................................... 4 Objectives of this Experiment ...................................................................................................... 4
CHAPTER 2: LITERATURE REVIEW ................................................................................................. 5 Nitrate Accumulation .................................................................................................................... 5
LITERATURE CITED ........................................................................................................................... 26
VITA ....................................................................................................................................................... 28
iv
LIST OF TABLES
Table 1 Percent emergence and seed source of 45 lettuce cultivars grown in years 1 and 2 ................. 10
Table 2 Growth parameters and nitrate content measured on individual lettuce heads grouped by the
four lettuce types evaluated in both years 1 and 2. ..................................................................... 13
Table 3. Average field weight (g) of individual lettuce heads evaluated in years 1 and 2. .................... 15
Table 4. Average height (cm) and width (cm) of individual heads evaluated in years 1 and 2. ........... 17
Table 5. Average leaf area (cm2) of individual heads of lettuce evaluated in years 1 and 2. ................. 20
Table 6.Top performing lettuce cultivars nitrate concentration (ppm) evaluated in years 1 and 2. ....... 21
v
ABSTRACT
Lettuce (Lactuca sativa L.) is an important leafy vegetable crop grown in worldwide food
systems with the United States ranking second behind China in total production. In 2009 the USDA
Food Economic Research Service reported 1,057,715 hectares of lettuce grown in the world. Lettuce is
a common market crop grown across the United States. Nitrate (NO3-) accumulation in lettuce and
other leafy vegetables has been found to be a potential health threat and when consumed by humans,
potentially causing methaemoglobinaemia and other diseases. There are four main types of lettuce and
numerous cultivars within each type. Fresh weight yields and nitrate accumulation may vary
significantly between lettuce types and/or cultivars, 45 cultivars of lettuce, representing the four types,
were grown in the field under best management practices at the LSU AgCenter Botanic Gardens in
Baton Rouge, LA, during Fall 2011 and Fall 2012. Based on field weight, recommended butterhead
cultivars were ‘Caliente’ (21.6 ppm) and ‘Harmony’ (13.9 ppm). The recommended green leaf
varieties were ‘Salad Bowl’ (10.6ppp) and ‘Tango’ (14.6 ppm). The recommended red leaf cultivars
were ‘Red Salad Bowl’ (15.2 ppm), ‘Red Sails’ (15.4 ppm), and ‘New Red Fire’ (24.0 ppm). The
recommended Romaine cultivar was ‘Green Towers’ (11.2 ppm) and the recommended crisphead
varieties were ‘Raider’ (17.6 ppm) and ‘Ithaca’ (14.9 ppm). When comparing the highest yielding
cultivars from the field weight study, ‘New Red Fire’ (24.0 ppm) produced the highest nitrate
concentration in both years 1 and 2. It made up 3.9% of the RfD (EPA’s maximum acceptable oral
dose of a toxic substance) for men and 4.59% of the RfD for women. This shows no concern for men
or women in the 20-74 age group.
1
CHAPTER 1: INTRODUCTION
History of Lettuce
Lettuce, Lactuca sativa L., is native to the Mediterranean area and inner Asia Minor and
was domesticated along the shores of Egypt around 4,500 B.C. It was grown throughout the
Mediterranean region and was commonly planted throughout the Roman Empire. During the 7th
century, lettuce cultivation was reported in China. Spanish explorers brought the plant to the
New World and by the 18th century it was widely used in the Americas (Swiader and Ware,
2002;Rubatzky and Yamaguchi, 1999).
Lettuce is an important leafy vegetable crop in current food systems. It is commonly
found on restaurant menus in the United States in the form of fresh salads and serves as a
common accompaniment for hamburgers, sandwiches, and tacos. When eaten fresh, it is an
excellent source of bulk and fiber (Swiader and Ware, 2002). In 2009, the per capita
consumption of lettuce was estimated to be 12.7 kg a year per person (USDA, 2011a). In the
U.S., Romaine lettuce and leaf lettuce production have increased 125 percent with 23,755
hectares planted in 1992 to 53,580 hectares planted in 2008 (USDA, 2011b; USDA2011c). Crisp
head lettuce production reduced in total acreage by 30 percent from 87,752 hectares planted in
1992 to 61,108 hectares planted in 2008 (USDA, 2011d). Following the potato, lettuce is one of
the leading fresh market vegetables in acreage, production, and value with California and
Arizona as the leading producers in the United States (Swiader and Ware, 2002). China leads the
worldwide agricultural community harvesting 12,855,500 metric tons in 2009 followed by the
United States and Spain harvesting 4,104,440 metric tons and 1,000,000 metric tons respectively
(USDA, 2011e).
2
Classification
Lettuce is classified into four groups: crisphead, butterhead, Romaine (Cos), and
looseleaf. Crisphead lettuce is also referred to as iceberg lettuce. Crisphead is characterized by
having a large, solid head weighing more than 907g and measuring more than 15cm in diameter.
The leaves are crisp and brittle with prominent veins and midribs. Crisphead is the more tolerant
of shipping and handling than all other types and therefore is the leading type of lettuce grown in
the U.S. (Swiader and Ware, 2002) despite a decline in production beginning in 1989 (USDA,
2011d). Romaine lettuce is characterized by long, narrow foliage, upright growth habit, and
loose, elongated heads. Butterhead lettuce is characterized by smooth, soft, and pliable leaves
forming a loose head. The veins and midribs of butterhead types are not as prominent as in
crisphead types and are considered to have better table quality and a more delicate flavor than
crisphead types. There are two subgroups of butterhead lettuce: Boston and bibb lettuce. Bibb
lettuce is smaller and darker green than Boston lettuce. Looseleaf lettuce is characterized as
producing an open rosette of leaves loosely arranged on the stalk. There is a considerable amount
of variation in leaf color within looseleaf lettuce, ranging from green and purple to red. There is
also variation in looseleaf texture and margin shape (Swiader and Ware, 2002). Although
lettuces vary in visual differences all subcategories assimilate and concentrate nitrate (NO3-) in
their leaf tissue. Nitrate is incorporated into proteins and other nitrogenous compounds and is
used as a terminal electron receptor in the respiratory chain of chloroplasts (Hill, 1996).
Nitrates
Nitrate (NO3-) is an integral component of the nitrogen cycle and is found throughout the
environment. The primary routes of entry of nitrates in human diet are drinking contaminated
ground water and oral ingestion of leafy vegetables (Hill, 1996). It is estimated that 80% of
3
dietary nitrates are derived from leafy vegetable consumption (Tamme, 2011). Although nitrate
itself at normal levels, below 3.7mg nitrate ion/kg body weight per day in the European Union
and below 1.6 mg nitrate nitrogen/kg body weight per day in the United States (EPA, 2012), has
not been proven to cause toxicological effects the nitrate metabolites, nitrite (NO2-) and N-
nitroso-compounds (NOCs) have profound toxicological effects on humans with some NOCs
listed as known carcinogens. Intestinal-type gastric cancer and methaemoglobinaemia are
extreme examples of diseases associated with high nitrate exposure (Hill, 1996). There are many
types of gastric cancer or stomach cancer that form in the stomach membrane. Adenocarcinoma
is the most common worldwide. In the US, 10,340 people died and 21,550 new cases of stomach
cancer were reported (NCI, 2011). The sole treatment for the gastric cancer is removal of the
stomach (gastrectomy) along with radiation therapy and chemotherapy to reduce reoccurance
(NLM, 2011). Methemoglobinemia is a blood disorder where abnormal amounts of
methemoglobin are produced in the body. Methemoglobin is a form of hemoglobin but differs by
not releasing oxygen to the body. It is commonly referred to as blue baby syndrome.
Methemoglobinemia is genetic or induced by the presence of certain drugs, chemicals or foods.
There are two forms of the genetic version. Form 1 can be found as Type 1 when red blood cells
completely lack the enzyme, cytochrome b5 reductase or Type 2 distinguished by the enzyme
being incompatible in the body. Form two is inherited genetically and is known as hemoglobin
M disease and is caused by defects to the hemoglobin molecule. Acquired methemoglobinemia is
more common, and occurs in people after they are exposed to particular chemicals including
nitrates. Infants and children can be vulnerable if they are fed excessive vegetables containing
high levels of nitrates such as Swiss chard, spinach, beetroot, celery, and squash (Santamaria et
al, 1999). These vegetables typically served in the form of pureed baby food.
4
Nitrate Accumulation
Nitrate accumulation in plant leaf tissue is influenced by the concentration in soil,
environmental conditions and by genotype. Reinink and Eenink (1988) report, low light
conditions increase nitrate concentration within leaf tissue. Lettuce genotypes with lower nitrate
concentration levels have been determined and are utilized in plant breeding programs. Reinink
(1991) introduced the concept of two genotype by environment (GE) interactions, daily
variations and annual variations. Nitrate assimilation in plants is the process by which nitrate is
converted and incorporated into carbon compounds within the plant such as pigments, lipids,
nucleic acids, or amino acids. Nitrate reductase catalyzes of the reaction for nitrate assimilation
and is regulated by several factors, one being light (Taiz and Zeiger, 2006). Thus nitrate
concentration may be determined by the duration and intensity of light during the fall and spring
crop cycles.
Objectives of this Experiment
1. Evaluate 45 lettuce cultivars to determine the highest yielding cultivars of each lettuce
type under typical commercial production standards in Louisiana.
2. Determine nitrate concentration in the foliage of the highest yielding lettuce types and
cultivars.
5
CHAPTER 2: LITERATURE REVIEW
Nitrate Accumulation
Nitrate content in leaf tissue of lettuce is influenced by genotype. Reinink et al. (1987)
evaluated 135 genotypes of lettuce for nitrate concentration. Two experiments were conducted.
In experiment 1 plants were grown on recirculating nutrient film and in experiment 2 plants were
grown in large pots containing potting soil. Nitrate content was determined using a Skalar
Autoanalyzer (Breda, The Netherlands). In both cultivated and wild lettuce genotypes,
differences in nitrate values were found. The highest nitrate values were in wild lettuce ranging
from 1.6 g/kg to 5.1g/kg fresh weight and the lowest nitrate levels were found in butterhead
types of cultivated lettuce ranging from 1.3g/kg to 3.7g/kg fresh weight. Ranges in plant dry
matter values were observed with wild lettuce genotypes averaging the greatest (8.7% and 9.4%
dry matter in experiment 1 and 2) and crisphead types of cultivated lettuce averaging the lowest
(6.9% and 6.8% dry matter in experiment 1 and 2. A negative correlation between nitrate content
and plant dry matter was observed in all lettuce types and the highest was observed within
butterhead lettuce types. As plant dry matter increased, nitrate content decreased. (Reinink et al,
1987).
In an attempt to determine differences in nitrate accumulation between leaf tissue and
root tissue, Reinink and Eenink (1988) conducted a study between nine different lettuce cultivars
grown in three different nitrate concentrations: 6.9, 10.5, and 13.5 mmol-3. Two Romaine
cultivars and seven butterhead cultivars were represented. Plant shoot tissue (leaves) and root
tissue were harvested and analyzed for nitrate content using a Skalar Autoanalyzer. Results
indicated that roots accumulated nitrate (nitrate content in root tissue was 4-9 times higher than
the nutrient solution) and the nitrate content of roots is closely correlated to the nitrate content of
6
shoots. However, differences in nitrate content observed among different cultivars were greater
in shoots than in roots. Thus, research focuses on nitrate content in shoots because lettuce roots
are generally not consumed. In 1991, Reinink studied two genotype by environment (GE)
interactions in Butterhead type lettuce: interactions related to daily variations in light intensity
and those related to annual variations in light intensity. Daily variations in nitrate content
influenced by light intensity were not detected however significant annual variations in nitrate
content caused by changes in light intensity were found. Burns et al. (2010) grew 24 cultivars of
lettuce from all four types including wild types inside a glasshouse during both winter and
summer months. Similar effects of genotype and light intensity were found. Nitrate content was
found to be higher in winter crops more so than summer grown crops.
In 2009, Novaes et al. analyzed nitrate content in lettuce between crops grown in soil and
crops grown in hydroponic conditions. The lettuce plants harvested from the hydroponic system
contained higher levels of nitrates (71.5 g/kg dry weight) than the field grown lettuce (29.8 g/kg
dry weight). Salomez and Hofman (2009) investigated nitrogen (N) nutrition and its effects on
shoot nitrate concentration in butterhead type lettuce grown in soil. The soil’s mineral N content
had a direct effect on shoot nitrate concentration. By using the lower suggested rates of 60 and
80 kg N/ha, nitrate concentration was reduced in 17 of 24 experiments and only decreased field
weight in 2 of the 24 experiments. Weightman et al. (2006) studied light level, time of harvest
and field position and their relation to nitrate concentration in lettuce. Short term shading had no
effect on nitrate accumulation but there were significant differences in time-of-day harvested in
contrast to Reinink in 1991. In 2010, Tamme et al. studied nitrate content of many leafy
vegetables and herbs including lettuce. Nitrate content of winter grown lettuce was 22% higher
than summer grown lettuce.
7
Hanafy et al. (2000) studied the effect of 4 bio-fertilizers on growth, yield, chemical
composition and nitrate accumulation of lettuce. All treatments received 100kg/fed (kg/0.41ha)